1. Field of the Invention
The present invention relates to a laser processing system using powder as filler material and being able to be used for laser overlay welding. The present invention also relates to an overlay welding method using the laser processing system.
2. Description of the Related Art
In recent years, the laser weld overlay using powder as filler material has been used for direct forming by near net-shape production, surface processing for giving a function of wear resistance or the like, and other purposes. The laser overlay welding needs precise control of the powder supply rate during processing in order to control the shape of the weld overlay and the chemical composition of the weld overlay in the case where multiple types of powders are used as filler materials.
However, since the powder supply rate is controlled by a powder supply device, the power transportation causes a time lag, so that it is difficult to precisely control the powder supply rate during processing. In addition, because of the time lag, the powder which is not used in welding is uselessly supplied to the region under the processing before and after the welding, so that the useless consumption of the powder lowers the yield.
In a technique which has been proposed for overcoming the above problem, the powder supply rate during processing is controlled by arranging, in a powder supply nozzle, a mechanism for controlling the powder supply rate. For example, Japanese Patent Laid-open No. 11-033757 discloses a powder supply device in which the rate of supply of powder from a powder supply nozzle is monitored and the powder supply rate is controlled by driving a nozzle pin upward or downward according to the monitored rate.
The above powder supply device supplies the powder from one side of the laser beam to the region under processing by making the powder drop from the nozzle by gravity. The powder supply device is constituted by a sensor which detects the flow rate of the powder discharged from the nozzle, a nozzle pin which controls the flow rate of the powder by being driven upward or downward in the nozzle, and a sensor which detects the position of the nozzle pin.
Nevertheless, the powder supply device having a construction as disclosed in Japanese Patent Laid-open No. 11-033757 cannot achieve a stable powder supply rate when the direction of the processing changes. In such a powder supply device, the structure of controlling the rate of fall of the powder with the nozzle pin can make the powder transiently pile up in the powder supply nozzle.
That is, the laser overlay techniques using the conventional powder supply device as described above has difficulty in quickly controlling the rate of supply of the powder to the region under processing, and is therefore unable to achieve a stable powder supply rate.
The present invention has been developed in view of the above circumstances. A first object of the present invention is to provide a laser processing system enabling quick control of the powder supply rate and achievement of powder supply rates which are more stable than the powder supply rates achieved in the laser overlay techniques using the conventional powder supply device. A second object of the present invention is to provide an overlay welding method using the above laser processing system achieving the first object.